However - consider that if you are using a fast exposure (macro) then the light is likely to be almost invisible. If you are using a slow exposure (wide angle or balanced light macro) then you should probably be using rear curtain synch, in which case the focus light will still be on during the exposure.

I shoot all macro, and use high-power 500 lm spotter lights as I don't see well in dim light. They don't cause any problems. Set up your camera inside, where it's warm, do a few different shots, and check them.

I recently added the Ikelite 2800 video light as a focus light (when not shooting video, @700 lumens) to my 2*ds125 strobes.
I glad to read it's not a big deal that the turn-off feature is not such an issue...

as I guessed from the beginning...

The great thing about it that it have a wide angel of coverage and even light.

It is generally pretty easy to tell whether it will be an issue or not before you take the shot. Look at the exposure meter in the viewfinder. If it is telling you the shot will be underexposed, you don't have to worry. If it's a stop or less underexposed, it might be an issue. If you're shooting macro, the exposure meter will almost always indicate underexposure (or you have too slow a shutter speed) and you should be fine, as Alex points out. It is only when you want to balance for ambient light that there might be an issue.